In modern cargo carrying airplanes, it is desirable to reduce the time required for loading and unloading cargo containers to an absolute minimum. The cargo is normally packaged in specially designed containers or pallets which are shaped to utilize all available space within the cargo compartment of the airplane. The cargo deck typically comprises a plurality of ball mats containing rollers balls to ease the passage of the cargo containers or pallets over the deck and into a final stowed position somewhere in the airplane. In many airplanes, cargo may be loaded through the nose section of the airplane and/or through a side cargo door.
During loading operations, the airplane cargo deck may not be precisely level. The crew must exercise care to assure that an unattended container or pallet does not slide, or roll back through the door opening. In order to keep the containers or pallets inside the airplane until they are secured to the main cargo deck, it is common practice to employ stop assemblies near the entrance or sill of the cargo door. In operation, the stop assemblies act like one-way gate assemblies that allow a cargo container or pallet to pass into or inboard the airplane but prevent passage of the container or pallet out of or outboard the airplane after the container or pallet has cleared the stop assembly.
A number of rollout stop assemblies have been designed and used for these purposes. For example, see the assemblies described in U.S. Pat. Nos. 3,698,679 and 4,375,932 to Lang, et al. and Alberti, respectively. These assemblies use complex linkages and are expensive to manufacture. Because of the complexity, reliability of the assemblies is not as high as customers demand. Finally, repair of these assemblies can be quite expensive.
The rollout stop assembly of U.S. Pat. No. 5,004,387 to Jensen, et al. comprises a stop rotatably mounted to a frame attachable to the cargo deck of an airplane proximate the sill of a side cargo door. The stop includes a vane that is spring biased to normally extend upwardly into the path of a cargo container being loaded in an inboard direction through the side cargo door. The vane has a spiral camming surface that, when: properly engaged by the container, causes the vane to rotate downwardly into the frame and out of the path of the container. Once the container passes the vane, it rotates back to its normal upward position whereby an abutment surface, forming part of the vane, may engage the container to prevent it from moving outboard of the airplane.
While the Jensen, et al. stop assembly is simple, relatively inexpensive to manufacture, and generally reliable, it may not always operate as intended. This can occur if the cargo containers warp upwardly about their periphery. Unfortunately, it is common for cargo containers to do so after extended use. As a consequence, the upwardly warped leading edge of a container may contact the spiral camming surface at an inboard high point where the moment arm that can be produced by the camming surface is low or negative. If the moment arm is too low, little or no downward rotation of the vane may result. When this happens, the cargo container is prevented from being loaded because the vane obstructs inboard motion.